Noise attenuation devices have heretofore been developed for the air induction systems of internal combustion engines.
One device used in such systems comprises an expansion chamber connected in the air intake flow path via an inlet and an outlet, the expansion chamber preventing the formation of large standing waves and absorbing acoustic energy. A venturi is sometimes formed in the inlet and/or the outlet to enhance performance of the expansion chamber and minimize the restrictive effect of the device on intake air flow.
See U.S. Pat. No. 5,163,387 issued on Nov. 17, 1992 for a "Device for Attenuating Standing Waves in an Induction Intake System" for an example of such a device.
The inlet and outlet include tube ends projecting in opposite directions into the expansion chamber, and these ends can have either an "overlapped" or "underlapped" relationship. When overlapped, the tube ends within the chamber extend past each other in the expansion chamber. In the underlapped condition, the tube ends within the chamber are separated from each other by a predetermined distance.
The noise in the air intake systems is composed of various harmonic orders, and which orders predominate depends on the rotational speed at which the piston engine is being operated, i.e., at higher speeds, the higher order harmonics of induction noise predominate, while at lower engine speeds, the lower order harmonics predominate.
It has been found that an underlapped or overlapped relationship of the inlet and outlet tubes has a basic effect on the noise attenuation function, i.e., the overlapped inlet and outlet tube configuration is effective in attenuating the fundamental and second orders of induction noise, while the underlapped configuration is effective in attenuating higher order harmonics.
Thus, if the overlapped configuration is used, the attenuation is less effective at higher engine speeds and, if the underlapped configuration is utilized, the device is less effective at lower engine speeds.
Accordingly, it is an object of the present invention to provide a resonator device of this type with improved effectiveness over a wide range of engine speeds.